In X11/Xorg's case, a common example would be environments built off different window managers, panels, launchers, etc. In theory nothing prevents Wayland to have something similar but in practice 17 years after its initial release, there isn't anything like that (or at least nothing that people do use).
At least in my mind, the Unix philosophy isn't some sort of dogma, just something to try and strive for and a base (like X11) that enables others to do that doesn't go against it from the perspective of the system as a whole.